Prior art piezoelectric transformers are based on the well known Rosen design (U.S. Pat. No. 2,830,274). These prior art transformer designs are of a piezoelectric ceramic plate which includes a driving section and a driven section which each have different polarizations. The different polarizations provide for the voltage transformation in these designs. However, these designs have several drawbacks. First, the piezoelectric plate must undergo special pre-processing in order to provide separately polarized sections. Second, the piezoelectric plate is limited in its power handling abilities. Third, in applications where a double-ended transformer design is needed, two transformers must be used having matched frequencies and impedances. However, it is very difficult to provide two resonators the have the same properties for all conditions, such as changing temperature and load conditions.
Generally, extensional mode resonators have opposing electrodes that cover essentially the whole top and bottom surfaces of a resonator substrate. In those applications requiring two resonators, such as in a double-ended transformer circuit, the resonators must be strongly coupled or of identical frequencies and impedance. Pairs of individual identical resonators can be made through tighter manufacturing tolerances and matching processes. However, both of these processes can be very costly.
The need exists for a new piezoelectric resonator which: includes strongly coupled oscillating sections, identical frequencies, and identical impedances that change similarly over time and temperature. In addition, it would be a benefit to provide these features in an simple, easily manufactured low cost device.